This invention relates to a cold cathode ion beam deposition apparatus with segregated gas flow, and corresponding method. More particularly, this invention relates to a cold cathode ion beam deposition apparatus wherein different gases are caused to flow through different flow channels toward an area of energetic electrons in order to provide a more efficient ion beam deposition apparatus and corresponding method.
An ion source is a device that causes gas molecules to be ionized and then focuses, accelerates, and emits the ionized gas molecules and/or atoms in a beam toward a substrate. Such an ion beam may be used for various technical and technological purposes, including but not limited to, cleaning, activation, polishing, etching, and/or deposition of thin film coatings. Exemplary ion sources are disclosed, for example, in U.S. Pat. Nos. 6,037,717; 6,002,208; and 5,656,819, the disclosures of which are all hereby incorporated herein by reference.
FIGS. 1 and 2 illustrate a conventional ion source. In particular, FIG. 1 is a side cross-sectional view of an ion beam source with a circular ion beam emitting slit, and FIG. 2 is a corresponding sectional plan view along section line IIxe2x80x94II of FIG. 1.
FIG. 3 is a sectional plan view similar to FIG. 2, for purposes of illustrating that the FIG. 1 ion beam source may have an oval ion beam emitting slit as opposed to a circular ion beam emitting slit.
Referring to FIGS. 1-3, the ion source includes hollow housing 3 made of a magnetoconductive material such as mild steel, which is used as a cathode 5. Cathode 5 includes cylindrical or oval side wall 7, a closed or partially closed bottom wall 9, and an approximately flat top wall 11 in which a circular or oval ion emitting slit 15 is defined. Ion emitting slit 15 includes an inner periphery 17 as well as an outer periphery 19.
Working gas supply aperture or hole 21 is formed in bottom wall 9. Flat top wall 11 functions as an accelerating electrode. A magnetic system in the form of a cylindrical permanent magnet 23 with poles N and S of opposite polarity is placed inside housing 3 between bottom wall 9 and top wall 11. The N-pole faces flat top wall 11, while the S-pole faces bottom wall 9 of the ion source. The purpose of the magnetic system, including magnet 23 with a closed magnetic circuit formed by the magnet 23, cathode 5, side wall(s) 7, and bottom wall 9, is to induce a substantially transverse magnetic field (MF) in an area proximate ion emitting slit 15.
A circular or oval shaped anode 25, electrically connected to positive pole 27 of electric power source 29, is arranged in the interior of housing 3 so as to at least partially surround magnet 23 and be approximately concentric therewith. Anode 25 may be fixed inside the housing by way of ring 31 (e.g., of ceramic). Anode 25 defines a central opening 33 therein in which magnet 23 is located. Negative pole 35 of electric power source 29 is connected to housing 3 (and thus to cathode 5) generally at 37, so that the cathode and housing are grounded (GR).
Located above housing 3 (and thus above cathode 5) of the ion source of FIGS. 1-3 is vacuum chamber 41. Chamber 41 includes evacuation port 43 that is connected to a source of vacuum (not shown). An object or substrate 45 to be treated (e.g., coated, etched, cleaned, etc.) is supported within vacuum chamber 41 above ion emitting slit 15 (e.g., by gluing it, fastening it, or otherwise supporting it on an insulator block 47). Thus, substrate 45 can remain electrically and magnetically isolated from the housing of vacuum chamber 41, yet electrically connected via line 49 to negative pole 35 of power source 29. Since the interior of housing 3 can communicate with the interior of vacuum chamber 41, all lines that electrically connect power source 29 with anode 25 and substrate 45 may pass into the interior of housing 3 and/or chamber 41 via conventional electrically feed through devices 51.
The conventional ion beam source of FIGS. 1-3 is intended for the formation of a unilaterally directed tubular ion beam 53, flowing in the direction of arrow 55 toward a surface of substrate 45. Ion beam 53 emitted from the area of slit 15 is in the form of a circle in the FIG. 2 embodiment and in the form of an oval (i.e., race track) in the FIG. 3 embodiment.
The ion beam source of FIGS. 1-3 operates as follows. Vacuum chamber 41 is evacuated, and a working gas 57 is fed into the interior of housing 3 via aperture 21. Power supply 29 is activated and an electric field is generated between anode 25 and cathode 5, which accelerates electrons 59 to high energy. Electron collisions with the working gas in or proximate gap or slit 15 leads to ionization and a plasma is generated. xe2x80x9cPlasmaxe2x80x9d herein means a cloud of gas including ions of a material to be accelerated toward substrate 45. The plasma expands and fills a region including slit 15. An electric field is produced in slit 15, oriented in the direction of arrow 55 (substantially perpendicular to the transverse magnetic field) which causes ions to propagate toward substrate 45. Electrons in the ion acceleration space in slit 15 are propelled by the known E x B drift in a closed loop path within the region of crossed electric and magnetic field lines proximate slit 15. These circulating electrons contribute to ionization of the working gas, so that the zone of ionizing collisions extends beyond the electrical gap 63 between the anode and cathode and includes the region proximate slit 15.
For purposes of example, consider the situation where a silane gas 57 is utilized by the ion source of FIGS. 1-3. The silane gas, including the silane inclusive molecules therein, passes through the gap at 63 between anode 25 and cathode 5. Unfortunately, certain of the elements in silane gas are insulative in nature (e.g., silicon carbide may be an insulator in certain applications). Insulating deposits (e.g., silicon carbide) can quickly build up on the respective surfaces of anode 25 and/or cathode 5 proximate gap 63. This can interfere with gas flow through the gap or slit, or alternatively it can adversely affect the electric field potential between the anode and cathode proximate slit 15. In either case, operability and/or efficiency of the ion beam source is adversely affected. In sum, the flow of gas which produces a substantial amount of insulative material buildup in electrical gap 63 on the anode and cathode may be undesirable in certain applications.
Moreover, electrical performance of the ion source is sensitive to parameters of gases within gap 63 (i.e., the electrical gap between the anode 25 and cathode 5). For example, electrical performance of the source is sensitive to characteristics such as the density of the gas within gap 63, the residence time of the gas within gap 63, and/or the molecular weight of the gas within gap 63. Changes in gas chemistry at gap 63 (intentional or unintentional) can alter the characteristics of ion beam 53 (e.g., with regard to energy and/or current density). This problem is particularly troublesome at high total flow conditions where the beam 53 can undergo a significant discontinuous transition between two operational modes (e.g., high energy/low current and low energy/high current).
U.S. Pat. Nos. 5,508,368; 5,888,593; and 5,973,447 relate to ion sources, each of these patents being hereby incorporated herein by reference. Unfortunately, the sources of the ""368, ""593 and ""447 patents primarily relate to thermionic emissive (hot) electron cathodes. This is undesirable, as cold-cathode sources such as that of the instant invention typically operate at higher voltages and/or lower gas flows. These advantages of cold-cathode sources translate into the ability to deposit much harder materials more efficiently (e.g., ta-C versus conventional DLC), and/or the need for fewer or less powerful pump(s). Additional problems with conventional ion sources are discussed in U.S. Pat. No. 6,002,208, in the context of the known Kaufman-type source (e.g., see col. 1 of the ""208 patent where it is indicated that such sources are disadvantageous in that they are not suitable for treating large surfaces and/or have low intensity).
In view of the above, it will be apparent to those skilled in the art that there exists a need for an ion source including a more efficient gas flow design.
An object of this invention is to provide a cold cathode closed drift ion source including a segregated gas flow system.
Another object of this invention is to provide a cold cathode ion source in which a one gas is caused to flow through the electrical gap between the anode and cathode toward an ion emitting slit, and another gas is caused to flow toward the slit but without much of said another gas passing through the electrical gap between the anode and cathode (i.e., preferably less than 50% of said another gas passes through this electrical gap, more preferably less than about 30%, and most preferably less than about 20%).
Another object of this invention is to provide a segregated gas flow arrangement in the context of a cold cathode ion source in order to reduce the likelihood of undesired insulative material buildups in the electrical gap between the anode and cathode.
Yet another object of this invention is to provide an ion source including a first gas flow path and a second gas flow path; wherein the first gas flow path accommodates the flow of a first gas toward the ion emitting slit and the second path accommodates the flow of a second gas (different from the first gas) toward the ion emitting slit.
Another object of this invention is to fulfill any and/or all of the aforesaid objects and/or needs.
Generally speaking, this invention fulfills any one or more of the aforesaid needs and/or objects by providing an ion beam source capable of emitting an ion beam toward a substrate, the ion beam source comprising:
a cathode;
an anode located at least partially between respective portions of said cathode, said anode including an inner periphery and an outer periphery;
an electrical gap defined between said anode and said cathode;
a magnet for generating a magnetic field proximate an ion emitting aperture defined in said cathode, wherein an ion beam is emitted toward a substrate from an area in or proximate said ion emitting aperture;
at least one first gas flow aperture or channel for enabling a first gas to flow around a periphery of the anode and through said electrical gap toward said ion emitting aperture; and
at least one second gas flow channel or aperture located within a body of said anode between inner and outer peripheries of said anode, said second gas flow channel or aperture for enabling a second gas to flow through said second gas flow channel or aperture toward said ion emitting aperture.
This invention further fulfills any one or more of the aforesaid needs and/or objects by providing An ion beam source capable of emitting an ion beam toward a substrate, the ion beam source comprising:
an anode and a cathode, with an electrical gap defined between said anode and said cathode;
at least one first gas flow aperture or channel for enabling a first gas to flow through said electrical gap toward an aperture or slit in said cathode; and
at least one second gas flow channel or aperture for enabling a second gas to flow through said second gas flow channel or aperture toward said aperture or slit without much of the second gas having to flow through said electrical gap.
Certain embodiments of this invention still further fulfill one or more of the aforesaid needs and/or objects by providing a method of emitting an ion beam toward a substrate, the method comprising the steps of:
providing an ion beam source including an anode and a cathode, so that an electrical gap is provided between the anode and cathode;
causing a first gas to flow through a first flow area around a periphery of the anode and through the electrical gap toward an aperture or slit defined in the cathode;
causing a second gas to flow through a second gas flow channel or aperture defined in a body of the anode and toward the aperture or slit in the cathode; and
ionizing at least a portion of at least one of the first and second gases proximate the aperture or slit in the cathode and causing an ion beam to be directed from the aperture or slit in the cathode toward the substrate.